Using β-ocimene to increase the artemisinin content in juvenile plants of Artemisia annua L

Advanced metabolic engineering strategies for increasing artemisinin yield in Artemisia annua L

Artemisinin, also known as 'Qinghaosu', is a chemically sesquiterpene lactone containing an endoperoxide bridge. Due to the high activity to kill Plasmodium parasites, artemisinin and its derivatives have continuously served as the foundation for antimalarial therapies. Natural artemisinin is unique to the traditional Chinese medicinal plant Artemisia annua L., and its content in this plant is low. This has motivated the synthesis of this bioactive compound using yeast, tobacco, and Physcomitrium patens systems. However, the artemisinin production in these heterologous hosts is low and cannot fulfil its increasing clinical demand. Therefore, A. annua plants remain the major source of this bioactive component. Recently, the transcriptional regulatory networks related to artemisinin biosynthesis and glandular trichome formation have been extensively studied in A. annua. Various strategies including (i) enhancing the metabolic flux in artemisinin biosynthetic pathway; (ii) blocking competition branch pathways; (iii) using transcription factors (TFs); (iv) increasing peltate glandular secretory trichome (GST) density; (v) applying exogenous factors; and (vi) phytohormones have been used to improve artemisinin yields. Here we summarize recent scientific advances and achievements in artemisinin metabolic engineering, and discuss prospects in the development of high-artemisinin yielding A. annua varieties. This review provides new insights into revealing the transcriptional regulatory networks of other high-value plant-derived natural compounds (e.g., taxol, vinblastine, and camptothecin), as well as glandular trichome formation. It is also helpful for the researchers who intend to promote natural compounds production in other plants species.

Engineering Saccharomyces cerevisiae for synthesis of β-myrcene and (E)-β-ocimene

Monoterpenes are among the important natural plant terpenes. Monoterpenes usually have the characteristics of volatility and strong aroma. β-Myrcene and its isomer (E)-β-ocimene are typical acyclic monoterpenes. They are high-value monoterpenes that have been widely applied in foods, cosmetics, and medicines. However, large-scale commercial production of β-myrcene and (E)-β-ocimene is restricted by their production method that mainly involves extraction from plant essential oils. Currently, an alternative synthetic route utilizing an engineered microbial platform was proposed for effective production. This study used a Saccharomyces cerevisiae strain previously constructed for squalene production as the starting strain. Farnesyl diphosphate synthase (Erg20) expression was weakened by promoter replacement and screened for optimal myrcene synthase (MS) and ocimene synthase (OS) activities. In the resulting S. cerevisiae engineered for β-myrcene and (E)-β-ocimene synthesis, titers of β-myrcene and (E)-β-ocimene were enhanced by a fusion expressing a mutant Erg20* with the obtained monoterpene synthase and optimizing the added solvent in a two-phase fermentation system. Finally, by scaling up in a 5-L fermenter, 8.12 mg/L of β-myrcene was obtained, which was first reported in yeast, and 34.56 mg/L of (E)-β-ocimene was obtained, which is the highest reported to date. This study provides a new synthesis route for β-myrcene and (E)-β-ocimene.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03818-2.

Cytotoxic and Antileishmanial Effects of the Monoterpene β-Ocimene

Leishmaniasis is a group of infectious-parasitic diseases with high mortality rates, and endemic in many regions of the globe. The currently available drugs present serious problems such as high toxicity, costs, and the emergence of drug resistance. This has stimulated research into new antileishmania drugs based on natural products and their derivatives. β-Ocimene is a monoterpene found naturally in the essential oils of many plant species which presents antileishmanial activity, and which has not yet been evaluated for its potential to inhibit the etiological agent of leishmaniasis. The aim of this work was to evaluate the activity of β-ocimene against Leishmania amazonensis, its cytotoxicity, and potential mechanisms of action. β-Ocimene presented direct activity against the parasite, with excellent growth inhibition of promastigotes (IC50 = 2.78 μM) and axenic amastigotes (EC50 = 1.12 μM) at concentrations non-toxic to RAW 264.7 macrophages (CC50 = 114.5 µM). The effect is related to changes in membrane permeability and resulting abnormalities in the parasitic cell shape. These were, respectively, observed in membrane integrity and atomic force microscopy assays. β-Ocimene was also shown to act indirectly, with greater activity against intra-macrophagic amastigotes (EC50 = 0.89 μM), increasing TNF-α, nitric oxide (NO), and reactive oxygen species (ROS), with lysosomal effects, as well as promoting decreases in IL-10 and IL-6. Against intra-macrophagic amastigote forms the selectivity index was higher than the reference drugs, being 469.52 times more selective than meglumine antimoniate, and 42.88 times more selective than amphotericin B. Our results suggest that β-ocimene possesses promising in vitro antileishmania activity and is a potential candidate for investigation in in vivo assays.

Phytohormone-Based Regulation of Trichome Development

Phytohormones affect plant growth and development. Many phytohormones are involved in the initiation of trichome development, which can help prevent damage from UV radiation and insect bites and produce fragrance, flavors, and compounds used as pharmaceuticals. Phytohormones promote the participation of transcription factors in the initiation of trichome development; for example, the transcription factors HDZIP, bHLH and MYB interact and form transcriptional complexes to regulate trichome development. Jasmonic acid (JA) mediates the progression of the endoreduplication cycle to increase the number of multicellular trichomes or trichome size. Moreover, there is crosstalk between phytohormones, and some phytohormones interact with each other to affect trichome development. Several new techniques, such as the CRISPR-Cas9 system and single-cell transcriptomics, are available for investigating gene function, determining the trajectory of individual trichome cells and elucidating the regulatory network underlying trichome cell lineages. This review discusses recent advances in the modulation of trichome development by phytohormones, emphasizes the differences and similarities between phytohormones initially present in trichomes and provides suggestions for future research.